The pushing off the rubber "debate" has been around since I began SETPRO. Back in the 90s Dick Mills, who at that time was probably the premier purveyor of pitching instruction, came out with a very successful advertising program where he called coaches who advocate pushing off the rubber is being brain-dead. As opposed to what Mills advocated which was pulling off the rubber. 10 years later he advocated a push to develop momentum.
Present day instruction such as TopVelocities 2X and 3X pitching systems advocate of what can only be described as pushing off the rubber. 3X defined as the extension of the leg caused by ankle-the-hip joint. The premise being that this "push" and subsequent blocking action of the plan foot and subsequent extension of the front knee is "somehow" converted into rotation to throw the baseball.
My estimate based on what I’ve seen on the Internet is that today at least 50% still believe pushing off the rubber is important for developing velocity and the other 50% have a number of different "beliefs" as to hat they may or may not call pushing off the rubber.
I have never been an advocate of pushing off the rubber. Why? Because from day one my physics background said that rotation is the key to throwing the baseball and it is virtually impossible for the body to efficiently and effectively convert linear momentum into rotational momentum. I’ve done a number of simulations showing that you cannot create rotation transverse plane of the body (the plane of the shoulders rotate in ) by blocking with the front leg. It is possible to create rotation in the sagittal plane (front to back i.e. bending forwards) but this is not an efficient mechanism for transferring momentum to the baseball. A topic which I will more fully discussed in the future.
I have long been an advocate that is not arm strength that creates velocity. Its momentum transfer. Rotation of the upper (large mass slow moving rotation) is then coupled to the arm (small mass fast-moving rotation) in a classic conservation of momentum process. Therefore the key to throwing efficiently is development of upper body rotational velocity.
My most recent focus has been on trying to quantify as well as qualifying those aspects of the pitching delivery that result in the most efficient transfer of momentum from the body to the baseball. In preparation for baseballthinktank’s Palooza 2016 I found the following article.
MacWilliams et al. (1998) indicated that push-off and landing leg forces acting on ground were related to linear wrist velocity at the ball release. That study concluded that pitching motion depends on significant contributions of the lower limbs to creating forward impetus of the body, contrary to the theory that pitching is a ‘controlled fall’.
We do not agree with their suggestion that building up push-off forces during the windup and braking forces of the leading foot to slow the motions of the body after foot contact would result in a proper energy transfer from the lower limbs to the trunk. They seem to explain that the momentum of the entire body increased before the leading foot contact is a primary energy source, while our study found that the system kinetic energy remarkably increased after stride foot contact, and most of the energy comes from internal joint work, and not from external work due to the joint forceinduced component.
In instep kicking, momentum of the whole body due to a running approach obtained before the kicking action is the primary energy source (Naito, Fukui, & Maruyama, 2012), while throwing utilizes positive power generated by the concentric activity of the trunk muscles after the landing foot contact as the more important energy source than the forward impetus of the legs. This fact supports the suggestion that increased trunk strength and flexibility (increased power of the trunk muscles) may improve a pitcher’s ability to generate pelvis and upper torso angular velocity, and consequently increase ball velocity (Matsuo et al., 2001).
Nevertheless, many investigations have referred to leg behavior as a key factor in improving throwing arm velocity (Chu, Fleisig, Simpson, & Andrews, 2009; Fleisig, Barrentine, Escamilla, & Andrews, 1996; Matsuo et al., 2001; Sachlikidis & Salter, 2007). The lower extremity strength is thought to be an important element of the baseball pitch (MacWilliams et al., 1998). We suppose that the leg joint moments would be necessary to assist a blocking mechanism that provides a stable base of support about which the trunk can rotate and allow the trunk to flex forward rapidly (Sachlikidis & Salter, 2007). In further studies, that concept should be confirmed by an improved model involving the lower extremity joints.
After reading this article I then located the article that is referred to "MacWilliams et al. (1998)"
Forces generated in the plane of the pitch were shown to be related to linear wrist velocity when the players were studied as a group. However, correlations between forces and wrist velocity within individual pitchers varied. Some players exhibited trends similar to the group, with wrist velocity increasing with increasing forces. Others demonstrated an opposite trend, with higher forces correlating with diminished velocities. This difference suggests that there may be an effect of attempting to overthrow, with loss of velocity resulting from attempts to generate unnaturally high push-off forces. This anecdotal information suggests that pitchers should train to develop powerful leg drives as a normal part of the throwing motion, but they should not attempt to overpush to gain extra velocity. The tendency of all pitchers in the study to develop high levels of force in the direction of the pitch, combined with the finding that pitchers who developed the largest forces (normalized to body weight) threw fastest, seems to contradict the theory that pitching is a "controlled fall." The pitching motion depends on significant contributions from the lower limbs to create forward impetus. The exact contributions of each segment to the pitching motion will require further study using a complex multisegmental dynamic model.
Based on this study, we hypothesize that the push-off forces in the direction of the pitch (AP shear) initiate the forward momentum of the entire body. The greater this magnitude, the more kinetic energy there is in the direction of the pitch. Similarly, the vertical push-off component can be used to generate potential energy, which can be transformed into kinetic energy at later stages. The landing leg serves as an anchor in transforming the forward and vertical momentum into rotational components; posteriorly directed forces at the landing foot reflect an overall balance of the inertial forces of the body moving forward to create ball velocities.
This information is important when training and developing efficient delivery to home plate. The high groundreaction forces generated in the throwing motion also support the concept that rehabilitation of pitchers with lower extremity dysfunction should be performed on level ground before returning to the mound. Further study of the relationship of these ground-reaction forces to the kinematics and kinetics of pitchers throwing other pitches would be beneficial. These studies may someday delineate those patterns that predispose an athlete to injury.